WATCH: The Lower Mainland is vulnerable to significant flooding that could cost billions of dollars in losses, according to a new report. Aaron McArthur explains what's driving risk factors, and the work being done to prevent a disaster.

If a major Fraser River or coastal flood happened in the Lower Mainland between now and 2100, it would be the most costly natural disaster in Canadian history, according to a new study.

For the past two years the study, commissioned by the Fraser Basin Council (FBC) for the Lower Mainland Flood Management Strategy (LMFMS), analyzed Lower Mainland flood scenarios and vulnerabilities along with a review of current flood protection.

The FBC says Lower Mainland flood risks are projected to worsen both in size and flood frequency over the next 85 years due to rising sea levels and climate change.

Present-day flood scenarios in the Lower Mainland would result in an estimated $20 to $23 billion loss and in 2100 the losses would be between $25 and $38 billion, for coastal and Fraser River flooding respectively.

“There’s a pressing need for climate change adaptation in how we plan communities, and the diking system is no exception.” said Colin Hansen, chair of the council, in a statement.

“We have to approach flood protection to address the new reality.”

The FBC admits the numbers are rough loss estimates based on a number of assumptions.

One main assumption is each of the flood-protected dikes in the area would fail during a major flood and the water would then spread freely. The study, which has one of two phases completed, found that Lower Mainland dikes were built in the 1970s and 1980s and were not designed for today’s climate change effects on flood risk.

According to a recent assessment by the Provincial Inspector of Dikes, it showed from the dikes examined that 71 per cent were vulnerable to fail from over-topping during a major Fraser River or coastal flood. Conversely, only four per cent of the assessed dikes met current provincial standards for dike crest height.

Phase 2 of the study, which received a $1 million contribution from the province, will focus on developing a regional flood action plan by 2018.